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Identification and activity of monoamine oxidase in the orb-weaving spider Larinioides cornutus
Rebecca J Wilson1, Tahmina H Ahmed2, Md Mahbubur Rahman3
1Department of Biological Sciences, East Tennessee State University, Johnson City, TN 37601, United States.
Abstract:
Monoamine oxidase (MAO) is a mitochondrial membrane-bound enzyme that catalyzes the oxidative deamination of monoamines in a wide array of organisms. While the enzyme monoamine oxidase has been studied extensively in its role in moderating behavior in mammals, there is a paucity of research investigating this role in invertebrates, where the latter utilizes this enzyme in a major pathway to degrade monoamines. There is especially a dismal lack of information on how MAO influences activity in invertebrates, particularly in account of the circadian cycle. Previous studies revealed MAO degrades serotonin and norepinephrine in arachnids, but did not investigate other critically important compounds like octopamine. Larinioides cornutus is a species of orb-weaving spider that exhibits diel fluctuations in behavior, specifically levels of aggression. The monoamines octopamine and serotonin have been shown to influence aggressive behaviors in L. cornutus, thus this species was used to investigate if MAO is a potential site of regulation throughout the day. Not only did gene expression of MAO orthologs and MAO activity fluctuate at different times of day, but the enzymatic activity was substrate-specific producing a higher level of degradation of octopamine as compared to serotonin in vitro. This study further supports evidence that MAO has an active role in monoamine inactivation in invertebrates and provides a first look at how MAO ultimately may be regulating behavior in an invertebrate.
Insights
Monoamine oxidase (MAO) regulates invertebrate behavior by degrading key neurotransmitters like octopamine and serotonin. This study reveals MAO activity fluctuates, impacting spider aggression across the day.
Area of Science:
- Biochemistry
- Neuroscience
- Arachnology
Background:
- Monoamine oxidase (MAO) is crucial for neurotransmitter metabolism in mammals, but its role in invertebrates, especially concerning circadian rhythms and behavior, is understudied.
- While MAO's degradation of serotonin and norepinephrine is known in arachnids, its substrate specificity and influence on compounds like octopamine remain unclear.
- Octopamine and serotonin are implicated in regulating aggressive behaviors in the orb-weaving spider Larinioides cornutus.
Purpose of the Study:
- To investigate the role of Monoamine oxidase (MAO) in regulating behavior in the orb-weaving spider Larinioides cornutus.
- To determine if MAO gene expression and enzymatic activity exhibit daily fluctuations.
- To assess the substrate specificity of MAO in degrading octopamine versus serotonin in vitro.
Main Methods:
- Quantified daily fluctuations in MAO ortholog gene expression and enzymatic activity in Larinioides cornutus.
- Performed in vitro enzymatic assays to measure MAO's degradation rates for octopamine and serotonin.
Main Results:
- MAO gene expression and enzymatic activity varied significantly across different times of the day in L. cornutus.
- In vitro assays demonstrated that MAO preferentially degraded octopamine over serotonin, indicating substrate specificity.
- These findings suggest MAO plays a role in the inactivation of monoamines in invertebrates.
Conclusions:
- Monoamine oxidase is actively involved in monoamine inactivation within invertebrates.
- MAO activity and substrate specificity may contribute to the regulation of daily behavioral patterns, such as aggression, in invertebrates like spiders.
- This research provides foundational insights into the neurobiological mechanisms underlying invertebrate behavior and circadian regulation.
